This invention relates to sound detecting apparatus.
The detection of the precise location at which noise is created, can aid in the improvement of a variety of devices, such as machine tools and air frames. For example, the design of an airframe or portion thereof, can be aided by placing a model in a wind tunnel to flow air over it, and scanning the model to determine locations that generate noise. An identification of the noise power as well as its precise location can provide a basis for determining whether relatively minor geometrical changes can reduce airframe noise. The detection of the noise can be accomplished by utilizing a large acoustic mirror facing a potential noise source, and utilizing the mirror to concentrate sound onto a microphone. However, the directionality or resolution of the mirror is limited by defraction effects arising from the fact that the wavelengths of noise of interest may not be small in comparison to the diameter of the mirror. A typical mirror utilized in this work is one meter in diameter. Although the resolution would be increased by increasing the mirror diameter, this would result in an unwieldy system because of the increased size and because the mirror must be supported upon a steerable structure for precisely orienting the mirror. Apparatus which allowed mirrors of relatively modest size to be utilized but which increase the resolution of such mirrors, would enable the more accurate determination of the locations from which sounds arise.